Effect of activated carbon on the color of green polyethylene terephthalate (PET) bottles

This study investigates the decolorization of recycled green PET bottles to enhance their recyclability and broaden their applications, particularly for high-purity and transparent materials. UV-Visible spectroscopy identified the green colorants in the PET as Solvent Green 5 (SG5), characterized by absorption regions between 400-460 nm and 580-720 nm, and Pigment Green 7 (PG7), further confirmed by X-ray photoelectron spectroscopy (XPS) which detected the presence of copper, chlorine and nitrogen. Three commercially available activated carbons (ACs) were characterized; the point of zero charge (PZC) was determined to be 2.37 for ACQR, and 7.6 and 7.98 for activated carbons MC and ME, respectively, revealing this parameter as the most influential factor in their dye adsorption capacity and selectivity. The decolorization process involved dissolving the recycled green PET, adsorbing the dyes onto the activated carbons, and separating the carbons from the PET. Colorimetric analysis of the resulting PET films showed that activated carbon content significantly impacts partial decolorization (56.15%), with ACQR preferentially adsorbing PG7, while activated carbons MC and ME primarily adsorbed SG5, demonstrably influencing the CIELAB color parameters ( L *, a *, b *). Thermal analysis indicated similar degradation behavior of the PET films between 400°C and 500°C; however, differences observed above these temperatures were attributed to variations in dye content. This approach demonstrates an effective method for PET decolorization, crucial for improving the quality and potential applications of recycled PET.